Fresh vs frozen donor eggs
What is egg freezing and how does it work?
Eggs are frozen using a technique called vitrification, which turns them into a glass-like state. Once in this state, eggs can be stored at very low temperatures for years without losing quality, until the patient is ready to start treatment.
After egg retrieval, before doing anything we look at the quality of the eggs. If the eggs are mature enough and of a high enough quality, then we freeze them using our vitrification system and store them at very low temperatures. To be able to do this well you need to have a very good vitrification system and experienced staff who are skilled in dealing with the cycle of egg freezing and thawing.
At London Egg Bank we have frozen more than 30,000 eggs, and we have also thawed more than 10,000 eggs. We’re always looking to improve our processes and monitor our results carefully. We’re delighted to see that our eggs have a 92% survival rate. The fertilisation of these frozen eggs is equally good and compares with a fresh egg rate, and we're seeing 70 - 80% fertilisation rates, sometimes more. And most importantly the number of embryos that we can create from these frozen eggs is above 50% in most cases.
Another very important factor that we always look for is what percentage of patients not only have embryos to use for their first treatment but to keep for further treatment later. Over 85% of our patients do have extra embryos frozen for this reason.
Since 2015 or 2016 we have converted completely into using frozen eggs, and vitrification has transformed the way we offer treatment to patients.
How do you assess the eggs for suitability?
Only eggs that are deemed mature and with a good chance of being usable at a later date are frozen. We look for the egg to have a good internal cytoplasm and a robust-looking polar body, which is a structure that tells us that the egg is mature. If the egg is mature, it means that it's at the right stage to be either frozen or inseminated with sperm so that it fertilises, but if it hasn't reached that stage it's not ready and needs more time. We don’t freeze immature or poor-quality eggs, only eggs that are of good quality, are mature and are ready to go.
Having a good vitrification system means that you don’t damage the egg, and so you don’t change their chromosomal arrangements or the DNA.
We’re interested not just in the egg survival rate, but also in the outcome of patients using frozen eggs. We’ve analysed live births from fresh and frozen eggs and have seen no difference. We've also looked at congenital abnormalities that were self-reported by the patient. While we can’t know of abnormalities that patients didn't report, we’ve looked at preterm births and any other implications that they might have had, and we couldn't see a difference when we compared fresh to frozen egg outcomes in our data.
Since we were established in 2013, London Egg Bank has consistently delivered the UK's highest recorded egg survival rates after freezing, at over 90% in all age groups. We’re delighted to see that our donor eggs have about 92% egg thaw survival rate. The fertilisation of these frozen eggs is equally good and compares with a fresh egg rate, and we're seeing 70 - 80% fertilisation rates, sometimes more. And most importantly the number of embryos that we can create from these frozen eggs is above 50% in most cases.
Why do some centres still prefer to use fresh eggs?
For some treatment centres their experience has been in using fresh eggs and having success with them, but where centres like ours have the experience and the scale of freezing eggs regularly, using frozen eggs carries as much success and more advantages than using fresh eggs alone.
If the embryologist and the laboratory are confident, consistently freeze eggs daily and are very familiar and highly skilled in the manipulation of this particular procedure, this makes the difference between preferring to deal with frozen as opposed to fresh eggs.
On our team the senior highly-skilled embryologist will freeze the eggs, relying on their expertise and experience to get the best results.
How does using frozen eggs improve patient care?
Vitrification is a relatively new process that has revolutionised the way that we manage and deal with egg donation. Previously, we were used to working with fresh eggs, which meant a degree of inconvenience for donors and recipients.
With fresh eggs, both the egg donor and the recipient have to be available at the same time, because they're both going through the treatment at the same time. Recipients were asked to take the contraceptive pill and the donor was asked to take the pill to regulate and synchronise cycles. The recipients also had to take an injection to create artificial menopause so that their natural cycle didn’t interfere with the process.
So much preparation was needed even before the treatment began, also it had some side effects, but it was all accepted as part of the programme.
And of course, with fresh egg donation, one can never be certain about the donor’s response to stimulation. Because in about 10% of cases, however, well the cycle is managed, the donor may not respond as well as we hope and that cycle would have to be abandoned, and so the recipient’s cycle would also have to be abandoned.
And again, at the time of egg collection, there were situations where we got fewer eggs than we expected. So there were times when the cycle may have to be stopped, abandoned, or it was weak or compromised. Simply because this was two women going through treatment together.
Now we can use frozen eggs with the same confidence as we used to have with fresh eggs, we have become used to a degree of convenience. Recipients can start treatment whenever they want. The donor has already finished her part of the treatment and the collected eggs are ready to be used at any time.
That is one major clinical development that has transformed the way we look at egg donation, and with the fantastic results that we are seeing, 50% clinical pregnancy per embryo transfer. This means that 50% of our recipients are getting pregnant when we put one embryo back, and 85% plus have more than one embryo from six eggs. This is a game-changer.
Does when eggs were frozen make a difference to the outcome?
When the eggs were frozen doesn't make any difference, because we have 24/7 monitoring equipment. All of our tanks, which store the frozen eggs in liquid nitrogen, are monitored and maintained 24/7. And we know the exact temperature and stability of the tank at any given time and ensure that all eggs are kept in optimum conditions. It doesn't make any difference as to whether they were frozen two years ago or two days ago.
When it comes to egg freezing fertility preservation, not egg donation, the HFEA, the UK fertility regulator, is looking to extend egg storage limits from 10 to 55 years. Without vitrification, this length of storage would never have happened, and the data is available to back up the confidence of this decision.
Does using frozen eggs affect the quality of frozen embryos?
No, the quality is not affected in any way by what we are seeing with our patients. We constantly monitor this because we have lots of patients that cannot have a fresh transfer for one reason or another, and so we use frozen embryos which are then transferred at a later date. In our results, we don't see any difference at all.
We're hitting over 50% success in the last year for frozen embryo transfers with frozen eggs. This is one of the reasons that in 99% of our cycles we only put one embryo back to reduce the risks of multiple pregnancies because freezing embryos is not a compromise.
Do you have experience with high sperm DNA fragmentation being an issue when using frozen donor eggs versus fresh ones?
We don’t see a significant difference between fresh and frozen eggs, but we look at every patient individually and we try to mould the treatment for them. So for example, if we have a patient with high DNA fragmentation, then there are ways that we can work around it, either with how we prepare the sperm or with the way that we're injecting the sperm into the egg to ensure that we have lower DNA fragmentation and a low percentage of oxidative stress.
Does transporting eggs affect success rates?
Most of our donors are recruited in London or Cardiff and then eggs are shipped to the right location when needed. Transporting eggs doesn’t affect their viability because we’re experienced with both national and international transport, using the same protocols.
It's very important to note that when we do transport eggs we monitor them very closely, so that we know everything about how they’ve travelled, whether there was any difference in temperatures, and so on, which means that there should be no difference in the outcome.
Shailaja Nair, Clinical Director
Dr Shailaja Nair is the Clinical Director and a founding member of London Egg Bank. She has more than 20 years' experience in fertility and assisted reproduction. Before joining London Women's Clinic, she worked in West London as an Associate Professor in a large teaching hospital and at the Cromwell IVF programme. Renowned for her passion, Dr Nair has extensive experience in all aspects of assisted conception, with a special focus on egg donation and cryobanking.
Elena Linara- Demakakou, Lab Manager and Quality Lead
Elena has 10 years’ experience in embryology and is qualified in biomedical sciences, prenatal genetics and fetal medicine, and clinical embryology. Her interests span from oocyte and embryo vitrification, prenatal genetics, and quality management, and she has gained valuable decade-long experience in intrauterine insemination. Before joining London Women's Clinic she worked as an embryologist, andrologist and as Deputy Sperm Bank manager.
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